1. Field of the Invention
This invention relates generally to a heavy duty axle unitized suspension and steering system for self powered chassis. The system embodied in this invention takes advantage of the unique location and connection of the steering gear to the Pitman arm and its location and connection by the primary drag link to the bell crank assembly, below and in-between the frame rails and above the axle. The primary drag link is located in a parallel plane and is the same length as the suspension arms when the trailer is moving forward in a straight line. This unique arrangement virtually eliminates the phenomenon known as bump steer and allows the wheels to turn at a high degree of steer, dramatically increasing maneuverability for long wheel base chassis.
Bump-steer is a change in toe angle caused by the suspension moving up or down. The effect of bump-steer is for the wheel to toe-in or toe-out when the suspension moves up or down. This toe change or “steering” occurs any time the suspension moves, whether it is from body roll, brake-dive, or hitting a bump in the road. Bump steer is undesirable because the suspension is steering the vehicle instead of the driver.
2. Prior Art
U.S. Pat. No. 5,220,972 Proia 1993 modifies existing self-tracking suspension systems that utilize toque rods to maintain the perpendicular orientation of the axle with respect to the center-line of the vehicle. Rubber bushings are installed on the ends of these torque rods to permit very limited angular movement as the vehicle turns. Multiple axle vehicles mount torque rods parallel to the longitudinal center-line of the vehicle body. This invention angles the forward ends of the torque rods inwardly towards the vehicle's center-line. Such angling of the torque rods allows the wheels to pivot as the trailer turns reducing wear on the drive tires and the road surface.
U.S. Pat. No. 5,234,067 Simard 1993 attempts to resolve long standing instability problems when dual axles are connected with leaf spring assemblies which are conventionally solved by the addition of torque rods as described in Proia above. His invention uses front and rear leaf-springs on each side that are aligned with each other and positioned forwardly and rearwardly of an equalizer beam. The front leaf-spring assembly has a front end pivotally attached by a pin to the vehicle frame and a rear end connected by a shackle to the front end of the equalizer beam. The rear leaf-spring assembly has a front end pivotally attached by a pin to the rear end of the equalizer beam and a rear end connected by a shackle to the frame of the vehicle. This allows road irregularity forces to be efficiently transmitted and stable without the use of torque rods.